The proposed design of a new 87Rb maser frequency standard is presented. This device is expected to perform similarly to a hydrogen maser at short and moderate averaging times. An operating maser of this design would much be more compact than a full size hydrogen maser (the cavity need only be ~6 cm in length and diameter). It should also be much less expensive to build. Optical pumping techniques are used to produce a nearly complete population inversion in an evacuated wall coated cell. The population inversion is produced in a cell separated from the microwave interaction region to eliminate problems with light shifts. Since no buffer gas is used the atoms are free to travel through an exchange tube from the optical pumping region to the maser interaction region where oscillation can take place. The system will be completely closed-cycle since atoms will return from the maser region to the optical pumping region where they will be repumped. This eliminates the need for a vacuum system, greatly simplifying operation. The principles of operation and the basis of the stability estimates are discussed

The United States Naval Observatory (USNO) has been using hydrogen masers for over six years as part of the USNO master clock. The Naval Research Laboratory (NRL) has also been using maser references as part of the NRL clock testing facility since September 1985. The masers discussed include the Smithsonian Astrophysical Observatory VLG-11, VLG-12, and masers from the Sigma Tau Standards Corporation. The authors describe the operation of the masers at USNO and NRL, including stability, aging rates, and reliability